A background technology of this technical field is Volume Shade Imaging (NPL 1). This NPL 1 indicates that more realistic and highly-visible volume rendering images can be generated by synthesizing volume data, depth information, and edge information.
Furthermore, NPL 2 describes a method of realistically rendering human skins and faces. When rendering a face by this method, the face is divided into three layers, that is, dermis, epidermis, and oil. Regarding the dermis and the epidermis, there is a method called “Sub-Surface Scattering” as a rendering method of reproducing a sense of high quality in computer graphics and this method is used for rending them. Sub-surface scattering is a method used, for example, when creating computer graphics of humans and is a technique to reproduce physical phenomena of light transmitting for a minute distance or diffusing on the skin surface. The oil is mainly a portion to reproduce reflections of a face.
Furthermore, NPL 3 describes a method of volume-rendering materials with a undersurface scattering property. This method is a method for creating light volume indicating how the light is irradiated on from the direction of a light source.